The present invention relates to thermoplastic elastomers with polyether units, and more particularly those containing also amide or polyester units. Elastomers with polyether and polyester units are, for example, those sold under the HYTREL trademark. As regards elastomers with polyether and amide units, in this family are found either elastomers having polyethers units and amide, oligoamide, and polyamide units randomly distributed, or elastomers formed by polyether blocks and by polyamide blocks. U.S. Pat. No. 4,207,410 describes the preparation of these random copolymers by reaction of a lactam or of an .alpha.,.omega.-aminocarboxylic acid with a polyether having hydroxy endgroups and a carboxylic diacid. U.S. Pat. No. 4,839,441 describes the preparation of polyether-polyamide block copolymers by reaction of a polyamide derived from a lactam with a carboxylic diacid and a polyether having hydroxy endgroups.
Depending on the conditions of synthesis and the purity of the raw materials, all these products may contain, to a greater or lesser extent, polyether, polyamide, or polyester oligomers and impurities which lower the viscosity, impair the transparency, or, occasionally, even exude. This exudation is all the greater when these copolymers are molded hot.